Multilayer capacitor

ABSTRACT

A multilayer capacitor includes a body in which a plurality of internal electrodes are stacked, including a ceramic sintered body; and external electrodes disposed on an external surface of the body and electrically connected to the internal electrodes. The ceramic sintered body includes a liquid pocket.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of priority to Korean PatentApplication No. 10-2018-0089914 filed on Aug. 1, 2018 in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND 1. Field

The present disclosure relates to a multilayer capacitor.

2. Description of Related Art

Multilayer capacitors have been used in various electronic components,and recently, in accordance with the digitalization of various functionsof technical fields requiring high reliability and an increase indemand, a high degree of reliability has been required in such amultilayer capacitor.

In order to improve the reliability of a multilayer capacitor, there isa need to secure structural stability. To this end, defects in a ceramicbody, internal electrodes, and the like, constituting the multilayercapacitor, should be significantly decreased.

A necessity for improving reliability of the multilayer capacitor hasbeen further increased in accordance with miniaturization of a device.There has been an attempt to develop various technologies for decreasinga thickness of internal electrodes or dielectric layers or improvingdispersibility of an additive in the art.

SUMMARY

An aspect of the present disclosure may provide a multilayer capacitorof which reliability is improved by controlling sintering properties, agrain size, and the like, of a ceramic sintered body forming a body.

According to an aspect of the present disclosure, a multilayer capacitormay include a body in which a plurality of internal electrodes arestacked, including a ceramic sintered body; and external electrodesdisposed on an external surface of the body and electrically connectedto the internal electrodes. The ceramic sintered body includes a liquidpocket.

The liquid pocket may be disposed at a grain boundary in the ceramicsintered body.

The liquid pocket may be disposed at a multiple grain boundary by atleast three grains adjacent to each other among a plurality of grainsincluded in the ceramic sintered body.

Among a plurality of grains included in the ceramic sintered body, agrain adjacent to the liquid pocket may have a smaller size than that ofa grain not adjacent to the liquid pocket.

Among the plurality of grains included in the ceramic sintered body, anaverage size of the grains adjacent to the liquid pocket may be smallerthan an average size of the grains that are not adjacent to the liquidpocket.

Among the plurality of grains included in the ceramic sintered body, anaverage size of the grains adjacent to the liquid pocket may be smallerthan a half of the average size of the grains that are not adjacent tothe liquid pocket.

A diameter of the liquid pocket may be within a range from 10 to 50 nm.

An average diameter of the liquid pocket may be within a range from 10to 50 nm.

The average number of liquid pockets per 1 μm² area of the ceramicsintered body based on a cross section may be within a range from 1 to10.

The average number of liquid pockets per 1 μm² area of the ceramicsintered body based on a cross section may be within a range fromgreater than 2 to 10.

The ceramic sintered body may further include a void.

The void may have a larger size than that of the liquid pocket.

The void may have a size of 0.1 to 10 μm based on a cross section.

The ceramic sintered body may be formed of a BT based ceramic materialand contain at least one of Si or Al ingredients as additioningredients.

An average interval between internal electrodes adjacent to each otheramong the plurality of internal electrodes may be 0.4 μm or less.

An average thickness of the plurality of internal electrodes may be 0.4μm or less.

The liquid pocket may be disposed in a dielectric layer separatingadjacent internal electrodes.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a partially cut-away perspective view schematicallyillustrating a multilayer capacitor according to an exemplary embodimentin the present disclosure;

FIGS. 2 and 3, which are schematic cross-sectional views of themultilayer capacitor of FIG. 1, are cross-sectional views taken alonglines A-A′ and B-B′ of FIG. 1, respectively;

FIG. 4 is an enlarged view illustrating some region (M region) of adielectric layer of a body of FIG. 2; and

FIGS. 5 and 6 are enlarged electron microscope images illustratingdielectric layers and internal electrodes of multilayer capacitorsobtained according to Inventive Example.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present disclosure will now bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a partially cut-away perspective view schematicallyillustrating a multilayer capacitor according to an exemplary embodimentin the present disclosure. FIGS. 2 and 3, which are schematiccross-sectional views of the multilayer capacitor of FIG. 1, arecross-sectional views taken along lines A-A′ and B-B′ of FIG. 1,respectively. FIG. 4 is an enlarged view illustrating some region (Mregion) of a dielectric layer of a body of FIG. 2.

Referring to FIGS. 1 through 4, a multilayer capacitor 100 according tothe present exemplary embodiment may have a structure including a body110 in which a plurality of internal electrodes 121 and 122 are stacked,including a ceramic sintered body, and external electrodes 131 and 132.In this case, the body 110 may include a liquid pocket 203 formed in theceramic sintered body.

A plurality of dielectric layers 111 may be stacked in the body, and thebody 110 may be obtained by stacking and sintering a plurality of greensheets as described below. The plurality of dielectric layers may beintegrated with each other by the sintering as described above. A shapeand dimensions of the body 110 and the number of stacked dielectriclayers 111 are not limited to those illustrated in the present exemplaryembodiment. For example, as illustrated in FIG. 1, the body 110 may havea rectangular parallelepiped shape. Even though the multilayer capacitor100 according to the present embodiment has a relatively small size,reliability thereof may be excellent. More specifically, the dielectriclayer 111 may have excellent insulation properties under a harshcondition. A thickness t1 of the dielectric layer 111, that is, anaverage interval between internal electrodes adjacent to each otheramong the plurality of internal electrodes 121 and 122 may be 0.4 μm orless.

The dielectric layer 111 included in the body 110 may contain a ceramicmaterial having high permittivity. For example, the dielectric layer 111may contain a barium titanate (BaTiO₃) based ceramic material, butanother material known in the art may also be used as long as sufficientcapacitance may be obtained. If necessary, the dielectric layer 111 mayfurther contain an additive, an organic solvent, a plasticizer, abinder, a dispersant, and the like, in addition to the above-mentionedceramic material corresponding to a main ingredient. Here, examples ofthe additive may include metal ingredients, and these metal ingredientsmay be added in a form of metal oxides in a manufacturing process.Examples of the metal oxide additive as described above may include atleast one material of MnO₂, Dy₂O₃, BaO, MgO, Al₂O₃, SiO₂, Cr₂O₃, andCaCO₃. In this case, elements forming a liquid phase during thesintering may be added in order to effectively form the liquid pocket203 in the ceramic sintered body as described below. For example, theceramic sintered body may contain a Ba ingredient, a Si ingredient, anAl ingredient, and the like, as addition ingredients.

Meanwhile, the body 110 may include an active region 115 formingcapacitance by the internal electrodes 121 and 122, and cover regions112 and 113 disposed on both sides of the active region 115 in athickness direction, that is, upper and lower surfaces of the activeregion 115 in FIGS. 1 through 3. Here, the active region 115 may includea capacitance region 116 in which the internal electrodes 121 and 122are disposed and a side margin region 114 in an outer portion in whichthe internal electrodes 121 and 122 are not disposed.

The cover regions 112 and 113 may serve to prevent the first and secondinternal electrodes 121 and 122 from being damaged by physical orchemical stress, and have substantially the same material andconfiguration as those of the dielectric layer 111 of the active region115 except that the internal electrodes 121 and 122 are not included. Inthis case, the cover regions 112 and 113 may be obtained together bystacking and sintering of green sheets. The cover regions 112 and 113 asdescribed above may be implemented in a sintered form by stacking one ortwo or more green sheets on the upper and lower surfaces of the activeregion 115.

The internal electrodes 121 and 122 may be connected to differentexternal electrodes 131 and 132 from each other to have differentpolarities from each other at the time of driving. As described below,the internal electrodes 121 and 122 may be obtained by printing andsintering a paste containing a conductive metal on one surface of aceramic green sheet at a predetermined thickness. In this case, theinternal electrodes 121 and 122 may be formed to be alternately exposedto both end surfaces of the body 110 in a stacking direction asillustrated in FIGS. 1 and 3, and may be electrically insulated fromeach other by each of the dielectric layers 111 interposed therebetween.Examples of a main ingredient constituting the internal electrodes 121and 122 may include nickel (Ni), copper (Cu), palladium (Pd), silver(Ag), and the like, and alloys thereof may also be used. The pluralityof internal electrodes 121 and 122 may become thinned so as to besuitable for miniaturization of the multilayer capacitor 100. Forexample, an average thickness t2 thereof may be 0.4 μm or less.

The external electrodes 131 and 132 may be formed on an external surfaceof the body 110 and may be electrically connected to the internalelectrodes 121 and 122, respectively. The external electrodes 131 and132 may be formed by a method of preparing a material containing aconductive metal in a form of paste and applying the paste on the body110, and examples of the conductive metal may include nickel (Ni),copper (Cu), palladium (Pd), gold (Au), or alloys thereof.

Referring to the enlarged view of FIG. 4, in the present exemplaryembodiment, the ceramic sintered body forming the body 110 may contain aplurality of grains 201 and grain boundaries 202 formed by the pluralityof grains 201, and the liquid pocket 203 may be formed in the grainboundary 202. More specifically, as illustrated in FIG. 4, the liquidpocket 203 may be formed at a multiple grain boundary by at least threegrains 201 adjacent to each other among the plurality of grains 201, forexample, a triple-point grain boundary. However, although FIG. 4illustrates some region M of the dielectric layer 111, other regions ofthe body 110, that is, the cover regions 112 and 113 and the side marginregion 114 may have a structure similar thereto.

The liquid pocket 203 may be formed between particles during sinteringthe dielectric layer 111, and thus, the liquid pocket 203 may have aneffect of suppressing grain growth of particles around the liquid pocket203. More specifically, in a case of mixing and sintering BT basedceramic particles, metal oxide additives, and the like, elements forminga liquid phase, for example, Ba, Si, Al, and the like, may form theliquid pocket 203 in a region between the particles. According to thestudy by the present inventors, a majority of the liquid pockets 203 asdescribed above may be formed in the triple-point grain boundary, andremain after the sintering by appropriately controlling sinteringconditions.

The liquid pocket 203 formed in the triple-point grain boundary mayserve to suppress additional grain growth while grain growth of thegrains 201 proceeds after densification is completed, such that amongthe plurality of grains 201, a grain adjacent to the liquid pocket 203may have a smaller size than that of a grain not adjacent to the liquidpocket 203. Therefore, an average size d1 of grains 201 adjacent to theliquid pocket 203 among the plurality of grains 201 may be smaller thanan average size d2 of grains 201 that are not adjacent to the liquidpocket 203. Further, the average size d1 of the grains 201 adjacent tothe liquid pocket 203 among the plurality of grains 201 may be smallerthan a half of the average size d2 of the grains 201 that are notadjacent to the liquid pocket 203. Here, the sizes d1 and d2 of thegrains may be defined as circle-equivalent diameters based on a crosssection.

The number and size of liquid pockets 203 may be adjusted depending on amaterial or a sintering condition of the ceramic sintered body, or thelike. For example, a diameter of the liquid pocket 203 may be within arange from 10 to 50 nm. Moreover, an average diameter of the liquidpocket 203 may be within a range from 10 to 50 nm. Further, in view ofan occurrence frequency of the liquid pocket 203, the number of liquidpockets 203 per 1 μm² area of the ceramic sintered body based on thecross section may be within a range from 1 to 10.

As described above, as fine grains 201 may be distributed due to thesuppression of grain growth around the liquid pocket 203, withstandvoltage properties and reliability of the dielectric layer 111 may beimproved. Here, reliability of the dielectric layer 111 may meanhigh-temperature acceleration and moisture resistance properties, andthe like. Describing the principle that the liquid pocket 203 remainsduring the sintering, first, in a green sheet for a dielectric layer, anadditive and a liquid phase are consumed in accordance with an increasein sintering temperature, and growth and densification of particlesproceed. For example, grain growth and densification of raw materials ofthe dielectric layer that are changed into liquid phases in a secondarycalcination environment of about 800 to 900 degrees proceed. To thisend, an additive containing an ingredient advantageous for forming aliquid phase such as Si, Al, or Ba may be used. Further, whiledensification of the particles proceeds, the liquid phase may remain insome regions such as boundaries between the particles, that is, theabove-mentioned triple-point grain boundary, and the like, such that theliquid phase may remain in a form of the liquid pocket 203 in a finalproduct. To this end, the sintering may be stopped in a state in whichthe liquid pocket 203 remains after the densification proceeds. Indetail, a sintering temperature which is about 1110° C. may be lowered,and a hydrogen concentration may be adjusted.

As described above, the liquid pocket 203 remaining in the dielectriclayer 111 may be detected during the sintering, and formed of a B—Si—Oingredient. In order to detect the liquid pocket 203 after themultilayer capacitor 100 is implemented, a surface of the dielectriclayer may be etched for analyzing a microstructure. In this process, theliquid pocket 203 may be removed. Even though the liquid pocket 203 isremoved, since a shape thereof may be different from a void, it may beconfirmed through electron microscopy analysis that the liquid pocket203 was present.

FIGS. 5 and 6 are enlarged electron microscope images illustratingdielectric layers and internal electrodes of multilayer capacitorsobtained according to Inventive Examples. In a dielectric layer 111included in a body, an etching region in which a liquid pocket 203 waspresent was observed in a ceramic sintered body, and the correspondingregion was indicated by a circle in FIGS. 5 and 6. Further, the ceramicsintered body may contain a void (V), and it was confirmed that ingeneral, a size of the void V was larger than that of the liquid pocket203. Based on a cross section, the size of the void V may be 0.1 to 10μm. Further, it was confirmed that a reflection region (a white regionin an edge of the void in FIGS. 5 and 6) was found in the edge of thevoid V due to morphological properties thereof at the time of capturingan image with an electron microscope, such that the void V and a site inwhich the liquid pocket 203 was present can be effectively distinguishedfrom each other.

Meanwhile, ceramic sintered bodies illustrated in FIGS. 5 and 6 wereobtained under different conditions from each other. In FIG. 5, about 25liquid pockets per 20 μm² were observed, and in FIG. 6, about 42 liquidpockets per 20 μm² were observed. Hence, the number of liquid pockets203 per 1 μm² area of the ceramic sintered body of FIG. 6 based on thecross section may be greater than 2. Samples of FIGS. 5 and 6 wereobtained using the same BT based ceramic particles as a raw material,and only additive ingredients were partially different from each other.In the sample of FIG. 6, an Al additive advantageous for forming aliquid phase was used. Therefore, in the sample of FIG. 6, the Alingredient was uniformly distributed in grains. Further, the samples ofFIGS. 5 and 6 were sintered by the same method, and a sinteringtemperature was set to about 1120° C.

As a result of performing a reliability test on the samples in whichoccurrence frequencies of the liquid pocket were different from eachother as described above, reliability was excellent in both the samplesas compared to the related art. However, the sample of FIG. 6 having alarger number of liquid pockets exhibited further improved reliability.In this case, a case in which resistance of the dielectric layer wasdecreased to about 10 to 10⁵Ω with the passage of time under harshconditions in the reliability test was considered as fail. As describedabove, it may be appreciated that when a relatively large number ofliquid pockets are present, reliability of the corresponding sample isexcellent. The reason may be that grain growth is suppressed around theliquid pocket as described above, such that the grain becomes atomized.

As set forth above, according to exemplary embodiment in the presentdisclosure, reliability of the multilayer capacitor may be improved bycontrolling the sintering properties, the grain size, and the like ofthe ceramic sintered body forming the body.

While exemplary embodiments have been shown and described above, it willbe apparent to those skilled in the art that modifications andvariations could be made without departing from the scope of the presentinvention as defined by the appended claims.

1. A multilayer capacitor comprising: a body in which a plurality of internal electrodes are stacked, including a ceramic sintered body; and external electrodes disposed on an external surface of the body and electrically connected to the internal electrodes, wherein the ceramic sintered body includes a liquid pocket, and wherein the liquid pocket is disposed at a grain boundary in the ceramic sintered body.
 2. (canceled)
 3. The multilayer capacitor of claim 1, wherein the liquid pocket is disposed at a multiple grain boundary by at least three grains adjacent to each other among a plurality of grains included in the ceramic sintered body.
 4. The multilayer capacitor of claim 1, wherein among a plurality of grains included in the ceramic sintered body, a grain adjacent to the liquid pocket has a smaller size than that of a grain not adjacent to the liquid pocket.
 5. The multilayer capacitor of claim 4, wherein among the plurality of grains included in the ceramic sintered body, an average size of the grains adjacent to the liquid pocket is smaller than an average size of the grains that are not adjacent to the liquid pocket.
 6. The multilayer capacitor of claim 5, wherein among the plurality of grains included in the ceramic sintered body, an average size of the grains adjacent to the liquid pocket is smaller than a half of the average size of the grains that are not adjacent to the liquid pocket. 7-8. (canceled)
 9. A multilayer capacitor comprising: a body in which a plurality of internal electrodes are stacked, including a ceramic sintered body; and external electrodes disposed on an external surface of the body and electrically connected to the internal electrodes, wherein the ceramic sintered body includes a liquid pocket, and wherein an average number of liquid pockets per 1 μm² area of the ceramic sintered body based on a cross section is within a range from 1 to
 10. 10. The multilayer capacitor of claim 9, wherein the average number of liquid pockets per 1 μm² area of the ceramic sintered body based on a cross section is within a range from greater than 2 to
 10. 11. The multilayer capacitor of claim 1, wherein the ceramic sintered body further includes a void.
 12. The multilayer capacitor of claim 11, wherein the void has a larger size than that of the liquid pocket.
 13. The multilayer capacitor of claim 11, wherein the void has a size of 0.1 to 10 μM based on a cross section.
 14. The multilayer capacitor of claim 1, wherein the ceramic sintered body is formed of a BT based ceramic material, and contains at least one of Si or Al ingredients as addition ingredients.
 15. The multilayer capacitor of claim 1, wherein an average interval between internal electrodes adjacent to each other among the plurality of internal electrodes is 0.4 μm or less.
 16. The multilayer capacitor of claim 1, wherein an, average thickness of the plurality of internal electrodes is 0.4 μm or less.
 17. The multilayer capacitor of claim 1, wherein the liquid pocket is disposed in a dielectric layer separating adjacent internal electrodes. 